1. Field of the Invention
This invention concerns a wiper blade rubber and, more specifically, it relates to a wiper blade rubber excellent in weather-proofness and, particularly, ozone cracking resistance with less frictional resistance upon sliding movement.
2. Description of the Prior Art
In FIG. 9, a wiper blade rubber is generally formed integrally as an elongate member comprising a base portion 10 of a large thickness, a swinging portion 30 substantially of a trigonal cross section, a neck portion 20 connecting the base portion 10 and the swinging portion 30, and a thin plate-like lip portion 40 disposed at the top end of the swinging portion 30. The base portion 10 is constituted with a head 11, a body 12 and a neck-like joining portion 13 connecting the head 11 and the body 12. The wiper blade rubber is inserted into a backing plate of a wiper and held while putting the backing plate provided between the head 11 and the body 12. Therefore the lip portion 40 moves slidingly on the glass surface for wiping out water droplets on the glass surface under the swinging movement of the swinging portion 30.
The wiper blade rubber as described above has been constituted with natural rubber (NR), or blended material prepared by blending NR with diene type rubber such as styrene-butadiene rubber (SBR), butadiene rubber (BR) and chloroprene rubber (CR).
Further, it has been known a method of chlorinating the surface or coating the surface with a surface layer containing lubricating fine powder such as molybdenum disulfide powder with an aim of reducing the frictional resistance upon sliding movement of the wiper blade rubber.
While the wiper blade rubber in the prior art as described above is excellent in the flexibility since the basic material is mainly composed of the diene rubber, it involves a disadvantage that the chemical double bonds of the constituent material are oxydized by ozone in the atmospheric air to result in crackings (ozone crackings). Because of the ozone crackings there has been a problem in the durability particularly, of the neck portion 20 to which the bending stress is exerted.
Further, although the chlorinated surface of the diene type rubber less causes ozone crackings, if the surface of the wiper blade rubber is entirely chlorinated, fitness to the uneven shape of the glass surface is worsened due to the rigidity of the wiper blade rubber. Accordingly, in the case of chlorination, it has been necessary to apply weak chlorination for the entire portion, or chlorination has to be excluded from the neck portion 20, however, in such the case, it becomes difficult to prevent the occurence of the ozone crackings. Further, the surface layer containing molybdenum disulfide powder or the like is not effective for preventing the occurence of the ozone crackings.
In the state where the wiper is not used, one side of the base portion 10 and the surface of the swinging portion 30 opposed by way of the neck portion 20 are urged to each other. If the blade is left as it is in this state for a long period of time, the base portion 10 and the swinging portion 30 may possibly be sticked to each other under the effect of sunlight or heat. If sticking occurs, turning of the swinging portion upon using the wiper becomes difficult so as to lower the wiping performance and the lip portion 40 tends to stand vertically thereby causing abnormal sounds due to the friction with the glass surface.